The paper describes an implementation of PBL methodologies in an undergraduate science course. In this course, students work with a voluntary environmental advocacy group, the Upper Chattahoochee RiverKeeper, to monitor the quality of water in the Chattahoochee watershed. Students learn experimental analytical chemistry techniques and problem-solving skills in this context. A PBL classroom is organized around collaborative problem-solving activities, which provide a context for learning and discovery. Students show enthusiasm and motivation to learn, and they achieve a deeper understanding of the material because it is information they have learned in a context of an interesting problem. PBL also provides them with an opportunity to acquire effective problem-solving techniques and to improve their communication skills and their ability to work in cooperative groups.